Hi Greg, On Fri, Dec 8, 2017 at 6:51 PM, Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Dec 08, 2017 at 06:00:47PM +0530, Vivek Gautam wrote: >> The device link allows the pm framework to tie the supplier and >> consumer. So, whenever the consumer is powered-on, the supplier >> is powered-on first. >> >> There are however cases in which the consumer wants to power-on >> the supplier, but not itself. >> E.g., A Graphics or multimedia driver wants to power-on the SMMU >> to unmap a buffer and finish the TLB operations without powering >> on itself. Some of these unmap requests are coming from the >> user space when the controller itself is not powered-up, and it >> can be huge penalty in terms of power and latency to power-up >> the graphics/mm controllers. >> There can be an argument that the supplier should handle this case >> on its own and there should not be a need for the consumer to >> power-on the supplier. But as discussed on the thread [1] about >> ARM-SMMU runtime pm, we don't want to introduce runtime pm calls >> in atomic paths, such as in arm_smmu_unmap. >> >> [1] https://patchwork.kernel.org/patch/9827825/ >> >> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx> >> --- >> drivers/base/power/runtime.c | 2 ++ >> 1 file changed, 2 insertions(+) >> >> diff --git a/drivers/base/power/runtime.c b/drivers/base/power/runtime.c >> index 027d159ac381..af169304ca13 100644 >> --- a/drivers/base/power/runtime.c >> +++ b/drivers/base/power/runtime.c >> @@ -1578,6 +1578,7 @@ void pm_runtime_get_suppliers(struct device *dev) >> >> device_links_read_unlock(idx); >> } >> +EXPORT_SYMBOL_GPL(pm_runtime_get_suppliers); > > We do not export symbols unless there are in-kernel users of them. > Where is the patch that adds a user for these functions? My apologies for not putting the changes for the user of these APIs. I will be sending a patch for the user (which would be: "drivers/gpu/drm/msm/msm_iommu.c"). The patch will be included with the arm-smmu runtime patch series. Right now I am facing issues with the use of clk_bulk_*() APIs on 4.15-rc kernel. But, I wanted to get opinions about this change since we had been discussing about this in the arm-smmu runtime patch thread [1]. [1] https://patchwork.kernel.org/patch/9827825/ P.S.: A snippet of the change in the user of these APIs: diff --git a/drivers/gpu/drm/msm/msm_iommu.c b/drivers/gpu/drm/msm/msm_iommu.c index b23d33622f37..1ab629bbee69 100644 --- a/drivers/gpu/drm/msm/msm_iommu.c +++ b/drivers/gpu/drm/msm/msm_iommu.c @@ -76,9 +76,9 @@ static int msm_iommu_unmap(struct msm_mmu *mmu, uint64_t iova, { struct msm_iommu *iommu = to_msm_iommu(mmu); - pm_runtime_get_sync(mmu->dev); + pm_runtime_get_suppliers(mmu->dev); iommu_unmap(iommu->domain, iova, len); - pm_runtime_put_sync(mmu->dev); + pm_runtime_put_suppliers(mmu->dev); return 0; } regards Vivek > > thanks, > > greg k-h -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
